A capacitor employed in an electronic device, for example, a dynamic random access memory (DRAM) device, can include a lower electrode, a dielectric layer and an upper electrode. In order to improve the capacitance of a memory device having the capacitor, increasing the electric capacitance of the capacitor can be important. Thus, the capacitor can have a flat shape so as to have a large capacitance; however, the shape of the capacitor has gradually changed to a box shape or a cylindrical shape to have a relatively large aspect ratio, for example, because the area of a unit cell of the DRAM device recently has reduced as integration of the DRAM device has increased to the giga-size range.
A cylindrical capacitor typically includes a lower electrode having a cylindrical shape. A buffer layer pattern may be used in a node-separation process to form the lower electrode having the cylindrical shape, and examples of materials that may be used for the buffer layer pattern include an oxide, a photosensitive material, etc.
In order to form the buffer layer pattern including an oxide, a buffer oxide layer can be formed through an oxide deposition process, and then the buffer oxide layer can be etched through an etch-back process or a chemical mechanical polishing (CMP) process. As a result, forming the buffer layer pattern can take a long time for the deposition process and the etching process. Additionally, a void may be formed in the buffer layer pattern. An atomic layer deposition (ALD) process can be required to form a buffer layer pattern without the void.
In order to form the buffer layer pattern including a photosensitive material, a photoresist film is formed. Thereafter, an exposing process, a developing process using a developing solution, a cleaning process and a baking process are typically sequentially performed on the photoresist film. High-cost exposure devices can be needed to form the buffer layer pattern. Furthermore, a baking process to harden the photoresist film at a temperature more than about 270° C. may be needed. A photoresist film hardened through a high temperature baking process may not be easily removed through a plasma ashing process.
Moreover, the lower electrode of the buffer layer pattern may be damaged while the ashing process and the cleaning process are performed. The buffer layer pattern may not be easily removed by a conventional ashing process, and residue of the buffer layer pattern that remains in an opening may serve as a resistance that causes the capacitor to malfunction. In order to improve the efficiency of the ashing process for removing the buffer layer pattern, an oxygen plasma ashing process may be performed at a temperature of about 150° C. to about 250° C. However, a high temperature ashing process may deteriorate and/or oxidize the lower electrode so the capacitor may not have a desired electric capacitance.